@Inherited 原注解功能介绍

@Inherited 底层

package java.lang.annotation;

/**
 * Indicates that an annotation type is automatically inherited.  If
 * an Inherited meta-annotation is present on an annotation type
 * declaration, and the user queries the annotation type on a class
 * declaration, and the class declaration has no annotation for this type,
 * then the class's superclass will automatically be queried for the
 * annotation type.  This process will be repeated until an annotation for this
 * type is found, or the top of the class hierarchy (Object)
 * is reached.  If no superclass has an annotation for this type, then
 * the query will indicate that the class in question has no such annotation.
 *
 * <p>Note that this meta-annotation type has no effect if the annotated
 * type is used to annotate anything other than a class.  Note also
 * that this meta-annotation only causes annotations to be inherited
 * from superclasses; annotations on implemented interfaces have no
 * effect.
 *
 * @author  Joshua Bloch
 * @since 1.5
 * @jls 9.6.3.3 @Inherited
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Inherited {
}

举例说明

代码

public class Inheritedtext {
    public static void main(String[] args) {
        //此时的 A.isAnnotationPresent(aa.class)；
	//意思就是：注释aa是否在此A上。如果在则返回true；不在则返回false。
        System.out.println(A.class.isAnnotationPresent(aa.class));
        System.out.println(B.class.isAnnotationPresent(aa.class));
        System.out.println(C.class.isAnnotationPresent(aa.class));
        System.out.println(D.class.isAnnotationPresent(aa.class));
    }
}
//定义注解aa
@Inherited
@Retention(RetentionPolicy.RUNTIME)
@interface aa{}
//被aa注解的类
@aa
class A{
}
class B extends A{
}
//未被aa注解的类
class C {
}
class D extends C{
}

结果

true
true
false
false

效果图

作用

如果一个类用上了@Inherited修饰的注解，那么其子类也会继承这个注解

注意

1. 接口用上个@Inherited修饰的注解，其实现类不会继承这个注解
2. 父类的方法用了@Inherited修饰的注解，子类也不会继承这个注解